This invention relates to electric motors and in particular, to a wound rotor for use in an electric motor.
Electric motors are very common in household appliances and hand held power tools. However, one modern trend is to make appliances smaller and lighter which requires smaller and lighter components including the electric motor which must maintain its output power.
Safe manufacturing regulations require certain safety standards to ensure consumer safety. Two of these requirements of concern in electric motor design are electrical clearance distance and electrical creepage distance. Electrical clearance distance is the minimum allowed distance between an electrically live part (such as the rotor windings) and a conductive part which could come into contact with the user, e.g., a motor shaft or metal housing. The creepage distance is similar to the clearance distance except that the distance is measured along the surface of the insulator supporting the live part, i.e., the windings.
As the size of the motor is reduced, the clearance and creepage distances are reduced as well, to the point where they are at the allowed minimum. However, further reduction in motor size is required, requiring careful consideration of clearance and creepage distance issues.
The present invention provides a way to reduce the overall length of the rotor without compromising the clearance and creepage distance requirements. This is achieved by providing a rotor which has a winding shield which has an integral axial extension which locates within an annular recess in a spacer which supports an end of the armature windings. The winding shield extends radially between the bearing and the armature winding to increase the creepage and clearance distances.
Accordingly, in one aspect thereof, the present invention provides a wound rotor for an electric motor comprising a shaft, a rotor core fixed for rotation with the shaft, a commutator fixed for rotation with the shaft and located adjacent one end of the rotor core, windings wound about poles of the rotor core and terminated on the commutator, a spacer of insulating material fixed to the shaft and located adjacent the other end of the rotor core and supporting an end of the windings and a radially extending winding shield fixed to the shaft and located at a first end of the spacer adjacent to the rotor core wherein the first end of the spacer has an axially extending recess and the winding shield has an axially extending tubular projection which is located within the recess of the spacer.
The shield of the rotor can be arranged to function as an oil slinger.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.